This experimental program at the University of Oregon has explored unique optical and transport properties of a special class of semiconductor heterostructures, so-called mixed-type quantum wells, consisting of a 2.5 nm thick GaAs layer (the narrow well) and a 16 nm thick GaAs layer (the wide well) separated by a thin AlAs layer about 10 nm in thickness.  The positively charged carriers of electrical currents in the narrow well, or holes, can tunnel through the AlAs barrier to the wide well.  Tunneling is a fundamental quantum mechanical process and is also essential to many semiconductor electronic devices.  Traditionally, tunneling has been considered as a transport process, with no connection to optical interactions.  The experimental studies carried out in this program, however, have discovered an effective mechanism, with which one can use a laser beam to control the tunneling process.  It was shown that optical excitations of the wide well with a laser beam can greatly accelerate the hole tunneling process, increasing the tunneling rate by up to two orders of magnitude.  More detailed studies indicate that Coulomb attractions between a hole in the narrow well and an exciton (which is essentially a hydrogen-atom like optical excitation in semiconductors) in the wide well can reduce the barrier of tunneling and thus accelerate the tunneling process.  The experimental studies were carried out at temperatures that are only a few degrees above the absolute zero.  If this type of phenomena can be extended to room temperature, one can envision designing semiconductor chips or logic gates that rely on or combine both optical and transport processes, which can potentially opening up many possibilities for applications. 

 This experimental program has also investigated properties of electron spins in diamond. Electron spins in diamond have shown great promise as solid-state qubits for quantum information processing.  The solid-state spin systems, however, are subject to flip flops of the surrounding nuclear spins, shortening the lifetime of the spin coherence and thus interrupting the coherent spin-photon interactions. In general, decoherence of a quantum state due to uncontrolled interactions with its environment puts a fundamental limit on applications of the relevant quantum technologies.  Experimental studies carried out in this program have realized a new approach for protecting an electron spin from environment-induced decoherence. This technique applies continuous microwave fields to a quantum system, dressing a spin with the microwave fields. The resulting hybrid spin-field states, called “dressed states,” can be incredibly insensitive to the system’s noisy magnetic environment.

 This research program has also made important contributions to education and human resource by providing training for one graduate student and two undergraduate students in areas of both scientific and technological importance.  In particular, research efforts supported by this program have led to one PhD dissertation.  In addition, the graduate student has also been highly actively in outreach activities such as tutoring science in rural elemental schools in Oregon. 

Last Modified: 11/19/2015
Modified by: Hailin Wang